1. Field of the Invention
This invention is a further development in the field of dual beam spectrophotometry, and in particular is directed to means for keying electronic circuitry for comparing signals from the separate channels of a spectrophotometer with the rotational motion of an optical chopper for directing radiation alternatively to the separate channels, where the rotational motion of the chopper may not be constant.
2. Prior Art
Heretofore, in dual beam spectrophotometry, where an optical chopper has been used to direct radiation alternately into two separate channels, various techniques have been used to provide pulsed signals wherein a particular temporal characteristic of a given pulse corresponds to a particular rotational position of the chopper. For example, the chopper disc could be encoded to generate a pulsed electrical signal wherein the pulses correspond temporally to the occurrence of particular optical events such as the passage of radiation into one or the other of the channels of the instrument. If a number of optical events are to be keyed to electronic circuitry, it was necessary in the prior art to encode the chopper disc, or some mechanical member whose motion is synchronized with the rotation of the chopper disc, in order to provide a separate pulsed signal for each optical event of interest. Typically, in the prior art, a number of light source and photocell pairs were used to provide an individual pulsed signal for each optical event being monitored.